Effect of atom transfer radical polymerization macroinitiator on properties of poly(meth)acrylate-based pentablock type of thermoplastic elastomers

We report well controlled synthesis of novel tri-component [polyisobutylene (PIB), poly(n-butyl acrylate) (PnBA) and poly(methyl methacrylate) (PMMA)] pentablock copolymers (PMMA-b-PnBA-b-PIB-b-PnBA-b-PMMA) by Atom Transfer Radical Polymerization (ATRP) using PIB as a macroinitiator. The surface properties (hydrophobicity, in vitro oxidative stability and cellular interaction) and the bulk properties (phase separation and mechanical properties) of the PIB-containing pentablock copolymers were compared with PMMA-b-PnBA-b-PDMS-b-PnBA-b-PMMA (where PDMS = polydimethylsiloxane) and conventional PMMA-b-PnBA-b-PMMA copolymers synthesized by PDMS and PnBA macroinitiators respectively. It is revealed that type of ATRP macroinitiator (with low glass transition temperature) influences the properties of resultant pentablock copolymers in terms of phase separation, mechanical properties in vitro oxidative stability, cytocompatibility and cell proliferation. Pentablock copolymers synthesized by PIB macroinitiator exhibited superior overall properties compared to pentablock copolymers synthesized by PDMS macroinitiator and neat triblock copolymer synthesized by PnBA macroinitiator. Among the copolymers tested, one with composition PIB:PnBA:PMMA = 10:64:26 (w/w) exhibited best mechanical property, oxidative stability and cytocompatibility. The newly designed PIB-containing pentablock copolymer may be useful where softness, flexibility, processability and biostability/cytocompatibility are desired.     

Synthesis and characterization of graft copolymers with poly(epichlorohydrin-co-ethylene oxide) as backbone by combination of ring-opening polymerization with living anionic polymerization

Series of graft copolymers with [Poly(epichlorohydrin-co-ethylene oxide)] [Poly(ECH-co-EO)] as backbone and polystyrene (PS), poly(isoprene) (PI) or their block copolymers as side chains were successfully synthesized by combination of ring-opening polymerization (ROP) with living anionic polymerization. The Poly(ECH-co-EO) with high molecular weight (M_n = 3.3 × 10⁴ g/mol) and low polydispersity index (PDI = 1.34) was firstly synthesized by ring-ROP using ethylene glycol potassium as initiator and triisobutylaluminium (i-Bu₃Al) as activator. Subsequently, by “grafting onto” strategy, the graft copolymers Poly(ECH-co-EO)-g-PI, Poly(ECH-co-EO)-g-PS and Poly(ECH-co-EO)-g-(PI-b-PS) were obtained using the coupling reaction between living PI⁻Li⁺, PS⁻Li⁺ or PS-b-PI⁻Li⁺ species capped with or without 1,1-diphenylethylene (DPE) agent and chloromethyl groups on poly(ECH-co-EO). By model experiment, the addition of DPE agent was confirmed to have an important effect on the grafting efficiency at room temperature. Finally, the target graft copolymers and intermediates were characterized by SEC, ¹H NMR, MALLS and FTIR in detail, and thermal behaviours of the graft copolymers were also investigated by DSC measurement.     

Living carbocationic polymerization of isobutylene and synthesis of ABA block copolymers by conventional laboratory techniques

Summary Living polymerization of isobutylene (IB) and subsequent controlled synthesis of ABA block copolymers, such as poly(styrene-b-isobutylene-b-styrene) (PSt-PIB-PSt) and poly(p-methylstyrene-b-isobutylene-b-p-methylstyrene) (PpMeSt-PIB-PpMeSt), have been carried out by a simple and inexpensive conventional laboratory technique. The homo- and block copolymers obtained by using this technique have exhibited excellent molecular weight control and low polydispersity indexes. The living nature of IB polymerization has been demonstrated by the incremental monomer addition (IMA) method with the dicumyl methyl ether (DiCumOMe)/TiCl₄ initiating system in the presence of 2,5-di-tert-butylpyridine (DtBP) proton trap. PSt-PIB-PSt and PpMeSt-PIB-PpMeSt block copolymers have been synthesized by sequential monomer addition: first living difunctional polyisobutylene (PIB) midsegment was prepared by difunctional initiator, then the second monomer was added to the charge. High blocking efficiencies and desired block copolymer structures have been obtained.     

Effect of PVC on low-polar isobutylene polymerization in the presence of BCl3

Summary The low-polar polymerization of isobutylene (IB) in the presence of BCI₃ was carried out in CH₂Cl₂ ([IB]=7 mol/l) at -78, -20 and +20°C in the presence of vinyl chloride/2-chloropropene (VC/2CP) copolymer, representing PVC resin enriched in structures with chlorine atoms bonded to the tertiary carbons. The polymerization products consist of mixtures of polyisobutylenes (PIB) and grafted VC/2CP-g-PIB copolymer. Attention was focused on evaluation of the extent of the grafting reaction. VC/2CP-g-PIB was analyzed by GPC, ¹H-NMR and ¹³C-NMR spectroscopies and elemental analysis. The results obtained indicate that the rate of polymerization of IB decreases with increasing temperature but that the grafting efficiency increases. The experiments demonstrated that the VC/2CP copolymer induces strong grafting, compared with PVC, and that it might therefore be assumed that the C-Cl bonds with chlorine atoms bound to tertiary carbons directly initiate the polymerization of IB. The effect of the C-Cl bonds is discussed in terms of their catalytic and initiation activities.     

Characterization and degradation of poly(vinyl chloride-g-lsobutylene) carrying tertiary chlorine and cyclopentadienyl branch termini

Summary Poly(vinyl chloride-g-isobutylene)s have been synthetized by using PVC backbones containing relatively high concentration of allylic chlorines [PVC(A)] in conjunction with BCl₃ coinitiator. Since graft-termination occurs by ion-collapse, graft copolymers with tertiary chlorine branch termini [PVC(A)-g-PIB-Cl] were formed. The presence of terminal tertiary chlorines has been demonstrated by degradation and cyclopentadienylation experiments. UV-visible spectra of ungrafted and grafted PVC(A) , molecular weight data, and branching frequency as a function of concentration of allylic chlorines indicate chain transfer to polyenes. Thermal and thermooxidative stability of PVC(A) increases upon grafting due to the replacement of allylic chlorines by PIB branches. The introduction of highly oxidizable Cp groups in PVC(A)-g-PIB-Cl by Me₂CpAl-treatment decreases the thermooxidative stability.     

Graft copolymerization of polyisobutylene and polychlorobutyl onto polystyrene waste

Poly(styrene-graft-isobutylene) (PS-graft-PIB) and poly(styrene-graft-chlorobutyl) (PS-graft-Cl-IIR) have been synthesized by the grafting of PIB and Cl-IIR onto polystyrene waste in conjunction with AlCl₃/HCl as catalyst. The grafting efficiency (GE) and overall graft composition have been studied. The synthesized graft polymers were purified and characterized by IR and ¹H NMR analysis. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were used to study the thermal characteristics of the graft. It is shown that the grafting induces better thermal stability for polystyrene. © 1999 Society of Chemical Industry     

Synthesis of polypropylene graft copolymers from a hydroxyl‐groups‐containing polypropylene precursor via atom‐transfer radical polymerization

Isotactic polypropylene graft copolymers, isotactic[polypropylene‐graft‐poly(methyl methacrylate)] (i‐PP‐g‐PMMA) and isotactic[polypropylene‐graft‐polystyrene] (i‐PP‐g‐PS), were prepared by atom‐transfer radical polymerization (ATRP) using a 2‐bromopropionic ester macro‐initiator from functional polypropylene‐containing hydroxyl groups. This kind of functionalized propylene can be obtained by copolymerization of propylene and borane monomer using isospecific MgCl₂‐supported TiCl₄ as catalyst. Both the graft density and the molecular weights of i‐PP‐based graft copolymers were controlled by changing the hydroxyl group contents of functionalized polypropylene and the amount of monomer used in the grafting reaction. The effect of i‐PP‐g‐PS graft copolymer on PP‐PS blends and that of i‐PP‐g‐PMMA graft copolymer on PP‐PMMA blends were studied by scanning electron microscopy. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of amphiphilic functional polyesters by ring-opening polymerization and click reaction

During this work we have prepared novel amphiphilic graft-block (PαN₃CL-g-alkyne)-b-PCL functional polyesters, comprising poly(α-azido-ε-caprolactone-graft-alkyne) (PαN₃CL-g-alkyne) as the hydrophilic segment and poly(ε-caprolactone) (PCL) as the hydrophobic segment, by ring-opening polymerization of ε-caprolactone (ε-CL) with hydroxyl-terminated macroinitiator PαClCL, substituting pendent chloride with sodium azide. The copolymers were subsequently used for grafting of 2-propynyl-terminal alkyne moieties by the Cu(I)-catalyzed Huisgen’s 1,3-dipolar cycloaddition, thus producing a “click” reaction. ¹H NMR, FT-IR, GPC, and differential scanning calorimetry (DSC) examined the characteristics of the copolymers. Grafting of PMEs or PMPEGs onto the PαN₃CL-b-PCL caused these amphiphilic copolymers to self-assemble into micelles in the aqueous phase. Fluorescence, dynamic light scattering (DLS) and transmission electron microscopy (TEM) then examined these micelles. The critical micelle concentration (CMC) ranged from 8.2 mg L⁻¹ to 39.8 mg L⁻¹ at 25 °C and the average micelle size ranged from 140 to 230 nm. The hydrophilicity and length of the hydrophilic segment influenced micelle stability. The current study describes the drug entrapment efficiency and drug loading content of the micelles, dependent on the composition of graft-block polymers. The results from in vitro cell viability assays indicated that (PαN₃CL-g-alkyne)-b-PCL shows low cytotoxicity.     

Synthesis and characterization of amphiphilic PLA-(PαN3CL-g-PBA) copolymers by ring-opening polymerization and click reaction

The present study prepared novel amphiphilic block-graft PDLLA-b-(PαN₃CL-g-PBA) and PLLA-b-(PαN₃CL-g-PBA) functional polyesters, containing a hydrophilic poly(α-azido-ε-caprolactone-graft-alkyne) (PαN₃CL-g-alkyne) segment and a hydrophobic poly(dl-lactide) (PDLLA) or poly(l-lactide) (PLLA) segment, using ring-opening polymerization of α-chloro-ε-caprolactone (αClCL) with a hydroxyl-terminated macroinitiator of PDLLA or PLLA, substituting pendent chloride with sodium azide. The copolymers were subsequently used for grafting of 2-propynyl-terminal benzoate moieties by way of Cu(I)-catalyzed Huisgen's 1,3-dipolar cycloaddition, thus producing a “click” reaction. Differential scanning calorimetry (DSC) and ¹H NMR, FT-IR, and GPC examined the characteristics of the copolymers. The critical micelle concentration (CMC) ranged from 2.7 mg L^?1 to 24.6 mg L^?1 at 25 °C and the average micelle size ranged from 106 nm to 297 nm. The length of the hydrophilic segment and the configuration of the lactide both influenced micelle stability. The micelle of PLLA-b-(PαN₃CL-g-PBA) provided high drug entrapment efficiency and loading content. The results from in vitro cell viability assays indicated that PLA-b-(PαN₃CL-g-PBA) shows low cytotoxicity.     

Synthesis and characterization of polytriphenylamine based graft polymers for photorefractive application

Novel graft copolymers, PTPA-g-PEAs containing poly(triphenylamine) (PTPA) backbone and poly(ethyl acrylate) (PEA) branches were synthesized by the oxidative coupling polymerization of triarylamine monomers followed by grafting of ethyl acrylate via an atom transfer radical polymerization (ATRP). Photorefractive (PR) composites based on the graft copolymers showed good static PR properties and fast response time under moderate conditions. The highest diffraction efficiency (19.7% at 45 V/μm) was observed with the composite containing the graft polymer with 18 mol% of graft density and 27 wt% of PTPA. And the fastest response (8 ms at 50 V/μm) was achieved when PTPA content was 68 wt%.     

Carbocationic polymerization in supercritical carbon dioxide

Polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) at 32.5°C and 140 bar by the use of 2-chloro-2,4,4-trimethyl-pentane (TMPCl) initiator in conjunction with a mixture of TiCl₄/BCl₃ leads to well-defined polyisobutylenes (PIB) capped by a t-Bu head group and a t-Cl tail group (tBu-PIB-Cl^t) of M_n1800 g/mole and M_w/M_n=1.3. The TiCl₄/BCl₃ mixture may be viewed a new Friedel-Crafts Acid that effects rapid initiation, essentially chaintransferless propagation and reversible termination. The mechanism of IB polymerization of TiCl₄/BCl₃ mixtures is discussed.     

Synthesis and characterization of mica—vinyl graft copolymers

Graft copolymerization of methyl methacrylate (MMA) and acrylonitrile (AN) onto mica was carried out by the ceric ion method. Experiments were carried out both in the presence and absence of oxygen; oxygen has some detrimental effect in the grafting of AN onto mica. Mica—vinyl graft copolymers were characterized using infrared spectra after purifying the crude graft copolymers for the removal of the occluded homopolymers. The percent grafting, grafting efficiency and the ratio of R_g/R_h were determined. Mica—graft copolymers were saponified by treating with aqueous alkali to convert the nitrile groups to carboxyl groups with a view to utilize these groups for coupling to collagen substrates. Since in a chrome-tanned leather there are available coordination sites due to fixed chromium, the mica—graft copolymer could get bound, thereby resulting in a well filled-up leather.     

Amphiphilic networks. XI. Mechanical properties and morphology

The bulk properties of two types of amphiphilic networks, poly(2-hydroxyethyl methacrylate)-l-polyisobutylene (PHEMA-l-PIB, H-network) and poly(N,N-dimethylacrylamide)-l-polyisobutylene (PDMAAm-l-PIB, A-network), have been investigated. Tensile strengths decreased considerably by swelling, and the decrease was more severe by swelling in water than in n-heptane. Elongations increased by swelling in water; however, the change was not consistent upon swelling in n-heptane. The hardness of dry networks decreased with increasing PIB content, while for wet networks it was similar to dry networks containing 85 wt % PIB. Small-angle X-ray scattering showed that average interdomain spacings decreased with increasing PIB content. According to dynamic mechanical thermal analysis (DMTA) the glass transition temperatures (T_g) of the respective hydrophobic and hydrophilic components shift toward each other with increasing PIB content. A “liquid-liquid transition” (T_ll) above the T_g of the hydrophilic component was apparent by DMTA, but could not be found by differential scanning calorimetry (DSC). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 901–910, 1997     

Living carbocationic polymerization

Summary Living carbocationic polymerization (LCPzn) of isobutylene (IB) has been achieved by the 2-chloro-2, 4, 4-trimethylpentate (TMPCl)/TiCl₄ initiating systems in the presence of KCl in conjunction with the 18-crown-6 ether in CH₂Cl₂/hexanes solvent mixture at –80°C. The rate of initiation is relatively slow and the molecular weight distribution (MWD) of the polyisobutylene (PIB) becomes narrower (M_w/M_n decreases from 1.8 to 1.2) in the course of incremental monomer addition (IMA). In the presence of the crown ether, and depending on its concentration, the charges become highly viscous rendering stirring difficult and preventing the synthesis of M_n's in excess of 15, 000 g/mole.     

Synthesis of graft copolymers from a linear polyolefin through a combination of coordination polymerization and atom transfer radical polymerization

This article reports on a facile route for the preparation of methyl acrylate and methyl methacrylate graft copolymers via a combination of catalytic olefin copolymerization and atom transfer radical polymerization (ATRP). The chemistry first involved a transforming process from ethylene/allylbenzene copolymers to a polyolefin multifunctional macroinitiator with pendant sulfonyl chloride groups. The key to the success of the graft copolymerization was ascribed to a fast exchange rate between the dormant species and active radical species by optimization of the various experimental parameters. Polyolefin‐g‐poly(methyl methacrylate) and polyolefin‐g‐poly(methyl acrylate) graft copolymers with controlled architecture and various graft lengths were, thus, successfully prepared under dilute ATRP conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Livig carbocationic polymerization

Summary Diblock copolymers of isobytylene (IB) — methyl vinyl ether (MeVE) have been prepared by sequential monomer addition by employing 2-chloro-2, 4, 4-trimethylpentane (TMPCl)/TiCl₄ initiating system in the presence of nBu₄NCl or dimethyl-acetamide (DMA) in CH₂Cl₂/hexanes at –80°C. In line with our earlier observations (1), living carbocationic polymerizations (LCPZn) were obtained in the presence of nBu₄NCl (i.e., the molecular weight of the poly(vinyl methyl ether) segment increased upon TiCl₄ addition), however, extensive chain transfer occurred in the presence of DMA. According to column chromatography analysis, the product prepared in the presence of nBu₄NCl is essentially pure PIB-b-PMeVE diblock (96w%) contaminated with a very small amount (4w%) of PIB. In contrast, the product obtained with DMA contains only 21w% PIB-b-PMeVe together with 72w% PIB and 5w% PMeVe homopolymers. This large difference in blocking efficiencies suggests that the structures of the growing species are different in the presence of the common anion salt,nBu₄NCl, and the electron donor, DMA.For paper LIII in this series see Polym. Bull., vol. 29/1     

Synthesis and characterization of a novel amphiphilic poly (ethylene glycol)–poly (ε-caprolactone) graft copolymers

A series of amphiphilic graft copolymers PEO-g-PCL with different poly (ε-caprolactone) (PCL) molecular weight were successfully synthesized by a combination of anionic ring-opening polymerization (AROP) and coordination-insertion ring-opening polymerization. The linear PEO was produced by AROP of ethylene oxide (EO) and ethoxyethyl glycidyl ether initiated by 2-(2-methoxyethoxy) ethoxide potassium, and the hydroxyl groups on the backbone were deprotected after hydrolysis. The ring-opening polymerization of CL was initiated using the linear poly (ethylene oxide) (PEO) with hydroxyl group on repeated monomer as macroinitiator and Sn(Oct)₂ as catalyst, then amphiphilic graft copolymers PEO-g-PCL were obtained. By changing the ratio of monomer and macroinitiator, a series of PEO-g-PCL with well-defined structure, molecular weight control, and narrow molecular weight distribution were prepared. The expected intermediates and final products were confirmed by ¹H NMR and GPC analyzes. In addition, these amphiphilic graft copolymers could form spherical aggregates in aqueous solution by self-assemble, which were characterized by transmission electron microscopy, and the critical micelle concentration values of graft copolymers PEO-g-PCL were also examined in this article.     

Graft copolymerization of poly(methyl methacrylate) with some alkyl methacrylates by atom transfer radical polymerization method and thermal properties

The preparation of graft copolymers of poly(methyl methacrylate) with some alkyl methacrylates were carried out via atom transfer radical polymerization method catalyzed by CuCl/2,2′-bipyridine and using a macroinitiator, poly[(methyl methacrylate)-co-(3,5-bis(chloroacetoxy)phenyl methacrylate)], including an amount of 1 mol % having α-halogeno carbonyl group in the side groups. Although the number-average molecular weights of a graft copolymer series of n-butyl methacrylate (n-ButMA) ended at different times increased from 55,700 to 99,500, the polydispersities decreased from 1.85 to 1.39 with time. The thermal degradation kinetics of macroinitiator and a two-armed graft copolymer of n-ButMA with this macroinitiator, PMMA-g-PnButMA: 4% (by mol), were carried out at different heating rates by thermogravimetric analysis and the results were compared. Using both the Flynn–Wall–Ozawa and Kissinger methods, the decomposition activation energies for macroinitiator were determined as 168 and 162 kJ/mol, respectively; they were also calculated as 233 and 239 kJ/mol for PMMA-g-PnButMA: 4%. The solid state thermodegradation mechanisms of both macroinitiator and PMMA-g-PnButMA: 4% are R₁-type mechanism, a phase boundary-controlled reaction, and F₁-type mechanism, a random nucleation with one nucleus on the individual particle, respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of poly(ɛ-caprolactone-b-isobutylene) diblock copolymer and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymer

Summary Poly(isobutylene-b-ɛ-caprolactone) diblock and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers have been prepared and characterized. The synthesis involved the living cationic polymerization of IB, followed by capping with 1,1-diphenylethylene or 1,1-p-ditolylethylene and end-quenching with 1-methoxy-1-trimethylsiloxy-2-methyl-propene to yield methoxycarbonyl functional PIB. Hydroxyl end-functional PIB polymers were quantitatively obtained by the subsequent reduction of methoxycarbonyl end-functional PIB with LiAlH₄. The structure of hydroxyl end-functional PIBs was confirmed by ¹H NMR and IR spectroscopy. Poly(ɛ-caprolactone-b-isobutylene) diblock copolymers and poly(ɛ-caprolactone-b-isobutylene-b-ɛ-caprolactone) triblock copolymers were synthesized by the living cationic ring-opening polymerization of ɛ-caprolactone with hydroxyl end-functional PIB as macroinitiator in the presence of HCl•Et₂O via the “activated monomer mechanism”. The block copolymers exhibited close to theoretical M_ns and narrow molecular weight distributions. Received: 30 January 2002/Revised version: 19 February 2002/ Accepted: 19 February 2002     

Slow initiation by tert-butoxybenzenes in living cationic polymerization of isobutylene

Summary tert-Butoxybenzenes including the 4-substituted derivatives of anisole, toluene and p-chlorobenzene have been synthesized and studied as initiators in combination with TiCl₄ for polymerization of isobutylene (IB) in CH₂Cl₂/methylcyclohexane (MeCHx) solvent mixtures at -78°C. Living polymerizations with slow initiation were observed by the allmonomer-in (AMI) and incremental monomer addition (IMA) techniques, and polymers with narrow molecular weight distribution (MWD) (M_w/M_n>1.1) were obtained under certain conditions. Aging of the initiating system prior to charging the monomer does not improve the initiating efficiency. It has been found that the initiating efficiency can be increased by increasing the solvent polarity, however, the relative volume of CH₂Cl₂ is limited in order to avoid polymer precipitation and bimodal MWD.